Valve lifters are used in internal combustion engines to convert rotational motion of an engine cam into linear motion, for controlling the position of gas exchange valves. A typical design includes a lifter body coupled with a pushrod configured to actuate a rocker arm of one or more gas exchange valves. The lifter body includes a roller positioned in contact with the engine cam, such that rotation of the engine cam causes the valve lifter to slide within a lifter bore formed in the engine housing. Sliding of the valve lifter adjusts the pushrod, which in turn moves the rocker arm in a well-known manner.
In certain designs, the roller may be generally cylindrical and contacts an outer surface of the cam, such that a desired interface between the roller and the cam outer surface is essentially linear. During service in the engine, valve lifters may become misaligned with the cam via rotation of the valve lifter within the lifter bore. The causes of such misalignment appear to vary from engine to engine. Even seemingly identical engine designs can exhibit different misalignment issues of their valve lifters over the course of the engine's service life. Adding to the complexity, some valve lifters tend to rotate more, or differently than other valve lifters even within the same engine.
Various strategies have been proposed over the years to limit rotation of valve train components. One technique employs an anti-rotation device received in an aperture formed in a skirt of a valve train tappet, such as that taught in U.S. Pat. No. 7,210,437 to Geyer. In Geyer, the anti-rotation device is mushroom-shaped and has a rectangular portion received in a rectangular aperture in the tappet. Geyer proposes preventing rotation of the tappet via guidance of the anti-rotation device in a groove intersecting a guide bore for the tappet. The design purportedly prevents radially inward excursions of the anti rotation device during service. While Geyer may achieve its stated purposes, it is not without drawbacks, and appears purpose-built to solve problems which may be specific to certain engine designs or duty cycles.